Radio-frequency transformer



NOV. 2, 1948. Q w RAMSDEN 2,452,679

RADIO FREQUENCY TRANSFORMER Filed April 16, 1945 INVEN TOR F IG. 5 By C. M. RAMSDEN ATTORNEY Patented Nov. 2, 1948 2,452,679 RADIO-FREQUENCY TRANSFORMER Clayton W. Ramsden, Elizabeth, N. J., assignor to Bell Telephone Laboratories,

Incorporated, New

York, N. Y., a corporation of New York Application April 16, 1945, Serial No. 588,682

Claims.

This invention relates to inductance devices particularly of the transformer type comprising inductively related primary and secondary windings.

An object of the invention is to provide means for adjusting the mutual inductance of two inductively related windings without changing the terminal connections for the windings.

A further object is to provide for the variation of the mutual inductance of two windings by an amount less than that which would be produced by the addition or removal of a complete turn of one of the windings.

In accordance with the preferred embodiment of the invention, the rimary winding comprises two spaced coils serially connected in opposing relation and the secondarywinding also comprises two spaced coils connected in opposing relation, each of the secondary coils surrounding one of the primary coils. With such an arrangement small changes in the mutual inductance of the windings may be readily produced by varyin the position of the connecting means between the adjacent turns of the two coils of the outer winding. For example, portions of the adjacent turns of the two coils of the outer winding may comprise parallel conductors of substantial crosssectional area and a cross-strap between said portions before permanent connection thereto may be adjusted to a position giving the desired mutual inductance. Such a mutual inductance adjustment is particularly advantageous since the mutual inductance may be varied without changing the terminal connections of the windings and thus permits a definite location of the circuit wiring for the device.

Referring to the drawings:

Fig. 1 is a side elevation of an inductive device embodying the invention;

Fig. 2 is another view of the device of Fig. 1 with the outer winding and the end portions broken away;

Fig. 3 is an end view partly in section of the device of Fig. 1 taken in the direction indicated by the arrows 3-3 of Fig. 1;

Fig. 4 is a schematic view of the winding arrangement of Fig. 1 illustrating the direction of the flux produced by the inner winding; and

Fig. 5 is a circuit diagram of the windings of Fig. 1.

Referring more particularly to Figs. 1 and 2, the transformer disclosed therein comprises a hollow cylinder or tube ID of insulating material surrounded by a two-section primary winding and a two-section secondary winding. One section of the primary winding comprises a ribbonshaped conductor spirally wound around tube I0 and extending between the terminal l2 and a metal strap I3 to which a mid-point terminal I4 is connected; the other section of the primary winding comprises a spirally wound ribbon-shaped conductor I5 extending between the metal strap I3 and the outer terminal Hi. The two conductors II and I5 are wound around the tube l0 and so connected as to produce opposing fluxes: and they may comprise the same number of turns so that terminal |4 provides a mid-point connection.

A second insulating tube surrounds the central portion of tube Ill and serves as a support for the secondary winding. If desired, the internal diameter of tube |l may be somewhat greater than the external diameter of tube ID in which case any suitable means may be provided for sup-' porting tube I! with its axis coinciding with the axis of tube l0. One section of the secondary winding mounted on tube comprises a single turn of a ribbon-shaped conductor .20 while the other section comprises a single turn of a ribbonshaped conductor 2|. As shown in Figs. 1 and 3, the two ends of each of the turns 20 and 2| are spaced apart slightly. One way in which the ends of the turns 20 and 2| may be fastened or terminated is shown in Fig. 3. Suitably mounted on tu-be I1 is an insulatin stri 22 having two slots 23 and 24, one for each turn. One end 25 of turn 2| passes under strip 22 up through slot 24 and then bent back on itself. The other end 26 of turn 2| after passing underneath strip 22 and upwardly through slot 2 3 is suitably formed to provide a terminal portion 2?. The ends of turn 20 are similarl formed around the slot 23 in strip 22 with one end of turn 20 being provided with a terminal 28. The ends of the turns 20 and 2| remote from terminals 2i and 28 are interconnected by a cross-strap 3| which may be adjusted to any desired position either close to slots 23. 24 or remote therefrom.

Schematic views of the windings are shown in Figs. 4 and 5. As previously described, the two primary windings sections H and I5 are connected in series opposiion so that the direction of the flux linking the primary and secondary windings may be represented by the two arrows 3.2, 33 of Fig. 4. But since the two sections 20 and 2| of the secondary winding are also connected in series opposition, it follows that the currents induced in the secondary winding sections 20 and 2| will be in aiding relation.

The above coil construction has special advantages when extremely close inductance requirements must be met in the primary winding since the mutual inductance of the two windings may be readily adjusted .to a desired value without changing the position of the terminals ii, i l, to, 2'? and 28 which are used for including the transformer in an electrical circuit. In making such an adjustment it is generally preferable to first adjust the selidnductance of the primary winding ll, 55 to the desired value, for example, by varying the positions with-in the winding sections of two cores 3?: and 35 made either of copper or a suitable magnetic material; Ihese two cores 3?), 35 are mounted on the ends of threaded rods 3? and 3d of non-magnetic material, such as brass, which are threaded through end pieces in tube it with their external ends being pro vided with knobs 3B and 68 whereby the rotation of rods 3?, Sid will produce longitudinal movements of cores 3? and 36 along the axis of the core tube ill. When these cores 35, 36 have been adjusted to provide the desired self-inductance for primary Winding H, is then the coupling between the primary and secondary windings may be adjusted by varying the location of the crossstrap 3i which connects turn 29 to turn 2i. the mutual inductance is less than the desired value when cross-strap Si is in the position shown in Fig. 1, the mutual inductance may be increased by moving strap 3i closer to ends 25, 30 of the turns 20, 2|; while if the position of strap 38 in Fig. 1 gives too large a mutual inductance, then the mutual inductance may be reduced by mov" ing strap 3| farther away from the end portions 25, 30. When the desired location of strap 3i has been determined it may be fastened, for example by soldering, to the winding turns and M. In making such an adjustment it is preferable that the connected points on turns 2B, 26 should be equidistant from the end'portions 25, so that the utilized fractional portion of turn 20 will exactly equal the utilized fractional portion of turn 2|. Strap 3| should also preferably lie parallel to the axis of tube Hi.

In the particular embodiment shown, each of the secondary winding sections consists of a single turn but obviously the invention may be applied to constructions where the inductive requirements are such as to require more than one turn in each secondary winding section. The inductive device of Fig. 1 may be supported in any suitable manner as, for example, by means of studs 42.

It will be understood that this invention is not limited to the specific construction herein illustrated and that the various features of the inven-.

tion may take various other forms within the scope of the appended claims.

The inductance device of this'in'vention possesses particular advantages for use in the high frequency field, for example, for frequencies of the order of 20 megacycles or higher.

What is claimed is:

1. A transformer comprising an insulating tube, a primary winding and a secondary winding surrounding said tube, said primary winding comprising a first coil and a second coil spaced from said first coil, said coils being serially connected so as to produce opposing fluxes, said secondary winding comprising a third coil and a fourth coll spaced from said third coil, said third and fourth coils being wound in opposite directions around said tube, and means for electrically connecting said third and fourth coils intermediate their ends to provide adesired mutual inductance for said primary and secondary windings.

'posite directions around substantially parallel to 2. A transformer comprising an insulating tube, a primary winding and secondary winding surrounding said tube, said primary winding comprising a first solenoidai coil and a second solenoidal coil spaced from said first coil, said coils being serially connected and wound in opsaid tube, said second ary winding surrounding said primary winding and comprising a third coil surrounding said first coil and a fourth coil surrounding said second call, the adjacent portions of said third and fourth coils comprising spaced substantially parallel con doctors, and means for fixing the coupling between said primary and secondary windings as desired, said means comprising a strap extending between the substantially parallel portions and intermediate the ends of said third and fourth coils and connecting said third and fourth coils in series opposition.

3. A transformer comprising an insulating tube, a primary winding and a secondary winding surrounding said tube, said primary winding comprising a first solenoidal coil and a second sclenoid-al coil spaced from said first coil, said coils being serially connected and wound in opposite directions around said tube, said secondary winding surrounding said primary winding and comprising a third coil surrounding said first coil and a fourth coil surrounding said second coil, the adjacent portions of said third and fourth coils comprising spaced substantially parallel conductors, and a cross-strap afllxed intermediate the ends of said coils electrically connecting said portions and lying substantially parallel to the axis of said tube, said cross-strap connecting said third and fourth coils in series opposition. 4. An inductance device comprising an insulating tube, a primary winding and a secondary winding surrounding said tube, saidprimary winding comprising a first coil and a second coil spaced from said first coll, said coils being serially connected so as to produce opposing fluxes, a pair of non-magnetic cores adjustable longitudinally along the axis of said tube, said secondary winding comprising a third coil surrounding said first coil and a fourth coil surrounding said second coil and spaced from said third coil and lying it, and a cross-strap for connection as desired intermediate the ends of said third and fourth coils and connecting them in series.

5. A transformer comprising an insulating tube,

a primary and a secondary winding surrounding said tube, said primary winding comprising a first coil and a second coil spaced from said first coil, said coils being serially connected so as to produce opposing fluxes, said secondary winding comprising a third, coil and a fourth coll spaced from said third coil, said third and fourth coils being wound in opposite directions around -said tube, means for adjusting the inductance of the primary winding, and means for fixing the coupling between the primary and secondary windings as desired to provide a desired mutual inductance,

CLAYTON W. RAMSDEN.

REFERENCES CITED 'The following references are of record in the file of this patent:

UNITED STATES PATENTS 

